1. Field of the Invention
The present invention generally relates to color separation elements and projection apparatuses, and more particularly to a color separation element for making a color separation and to a projection apparatus which projects an image on a screen using such a color separation element.
A projection apparatus which displays an image by projecting a light obtained via a liquid crystal display on a screen is used as a display unit of television systems, video systems, information display systems and the like.
2. Description of the Related Art
FIG. 1 is a diagram showing an important part of an example of a conventional projection apparatus. In FIG. 1, a light from a light source 101 is supplied to a projection lens 103 via a dichroic mirror optical system 102, and an image is displayed on a screen (not shown) by projecting the light from the projection lens 103 on the screen. The dichroic mirror optical system 102 includes dichroic mirrors (DM) 121 through 124, liquid crystal panels 125 through 127, and mirrors 128 and 129.
A red (R) light within the light from the light source 101 is transmitted through the dichroic mirror 121, reflected by the mirror 128, transmitted through the liquid crystal panel 125 which displays R pixel data and the dichroic mirror 123, and reaches the projection lens 103 by being reflected by the dichroic mirror 124. A green (G) light within the light from the light source 101 is reflected by the dichroic mirrors 121 and 122, transmitted through the liquid crystal panel 125 which displays G pixel data, and reaches the projection lens 103 by being reflected by the dichroic mirrors 123 and 124. A blue (B) light within the light from the light source 101 is reflected by the dichroic mirror 121, transmitted through the dichroic mirror 122 and the liquid crystal panel 127 which displays B pixel data, and reaches the projection lens 103 by being reflected by the mirror 129 and then transmitted through the dichroic mirror 124.
FIG. 2 is a diagram showing an important part of another example of the conventional projection apparatus. In FIG. 2, those parts which are the same as those corresponding parts in FIG. 1 are designated by the same reference numerals, and a description thereof will be omitted. In FIG. 2, the R light within the light from the light source 101 is reflected by a dichroic mirror 131, and reaches the projection lens 103 via a lens array 134, a RGB liquid crystal panel 135 and a condenser lens 136. The G light within the light from the light source 101 is transmitted through the dichroic mirror 131, is reflected by a dichroic mirror 132, and reaches the projection lens 103 via the lens array 134, the RGB liquid crystal panel 135 and the condenser lens 136. In addition, the B light within the light from the light source 101 is transmitted through the dichroic mirror 132, is reflected by a dichroic mirror 133, and reaches the projection lens 103 via the lens array 134, the RGB liquid crystal panel 135 and the condenser lens 136. For example, the projection apparatus of this type is proposed in a Japanese Laid-Open Patent Application No.4-60538.
In the case of the conventional projection apparatus shown in FIG. 1, the dichroic mirror optical system 102 includes the four dichroic mirrors 121 through 124, the three panels 125 through 127, and the two mirrors 128 and 129. Hence, there were problems in that the number of parts is large, it is difficult to reduce the size of the projection apparatus, and it takes time to adjust mounting positions of each of the large number of parts.
On the other hand, in the case of the conventional projection apparatus shown in FIG. 2, the construction of the optical system is slightly simpler when compared to the conventional projection apparatus shown in FIG. 1. However, it is still necessary to provide the three dichroic mirrors 131 through 133, and each of the dichroic mirrors 131 through 133 must be mounted to satisfy a predetermined relationship with respect to the incident angle of the light from the light source 101. As a result, there was a problem in that it takes time to adjust the mounting positions of each of the parts.
Moreover, in the conventional projection apparatuses shown in FIGS. 1 and 2, the color separation element has a complex construction, and it requires troublesome and time consuming processes to mount the elements which form the color separation element and to adjust the mounting position thereof. For these reasons, there are also demands to realize a color separation element which has a simple construction and can be easily mounted and easily be adjusted of the mounting position.